PRACTICAL CONSIDERATIONS : THE WRIST-JOINT. 



329 



Metacarpals 



on the dorsum of the os magnum is distinct, and some indication of the mid-carpal 

 joint may be felt near it. " Slightly external to the middle of the hand is a promi- 

 nence, sometimes indistinct, but often very well marked, formed by the styloid 

 process on the base of the third metacarpal bone at its articulation with the os 

 magnum" (Thane and Godlee). On the palmar side the pisiform can be felt just 

 at the beginning of the hypothenar eminence. When the hand is flexed and the 

 muscles relaxed, it is easily moved from side to side. The unciform process can 

 be indistinctly felt below it. 



The tubercle of the scaphoid Fig. 351. 



is felt with difficulty below 

 and internal to the radial 

 styloid, and at the beginning 

 of the thenar eminence (the 

 ridge on the trapezium) more 

 clearly. The position of the 

 annular ligament may be de- 

 duced from these points, and 

 it may be felt by pressure on 

 the hand. It is a general rule 

 for the joints between the meta- 

 carpals and the phalanges, as 

 well as for those between the 

 latter, that the more distal 

 moves on the proximal, and 

 that, therefore, the promi- 

 nence of the knuckle in flexion 

 is made by the head of the 

 metacarpal. All the meta- 

 carpo-phalangeal joints can be 

 made out from the dorsum. 

 The sesamoid bones of the 

 thumb are felt with difificulty. 



. The web of the fingers lies about thirteen millimetres distal to the palmar aspect of 

 the metacarpo-phalang^al joints. That of the index-finger is about midway between 

 the transverse furrow reaching the radial side of the hand and the first crease on 

 the finger ; those of the other fingers are in the same relation to the second furrow 

 and the respective creases. The interdigital joints are slightly distal to the upper 

 line of the complicated creases of the first joints and to the single line of the creases 

 of the second row. 



Sheath for flexor 

 tendons opened 



Transverse metacarpal ligament 



Palmar aspect of right metacarpo-phalang:ea! joints. Sheath for flexor 

 tendons on one finger opened ; on adjacent finger still closed. 



PRACTICAL CONSIDERATIONS. 



The Wrist-Joint. — The radio-carpal has the greatest amount of motion of 

 the three rows of joints that intervene between the metacarpus and the forearm. Its 

 strength is not derived from the shallow concavity on the lower end of the radius, 

 or from the ligaments which, taken together, compose the capsule, but rather from 

 the tough fibrous tissues forming the sheaths of the large number of tendons that 

 pass over the anterior and posterior aspects of the joint and are closely united to 

 the bones. It escapes frequent injury, also, because of the numerous bones that 

 enter into the carpus, which by their gliding motion one upon the other diffuse force 

 received through falls upon the hand ; because of the same effect produced by the 

 movement of the mid-carpal joint (intracarpal of Dwight), which takes up part of the 

 force in overextension of the hand before it reaches the wrist ; and because of the 

 absence of any long rigid lever on the distal side of the joint. 



Dislocation backward is by far the most common, on account of the frequency 

 of falls upon the hand. The diagnosis from CoUes's fracture is made by observing 

 that in dislocation : (i) the anterior swelling is nearer the ball of the thumb ; (2) 

 the posterior swelling is more sharply defined at its upper edge ; (3) the styloid 

 process of the radius is nearer the hand than that of the ulna .; (4) the distance from 



